The present invention relates to a bipolar transistor and a method for fabrication the same, and more particularly relates to a structure for a high-performance bipolar transistor including a hetero-junction such as Si/SiGe and Si/SiGeC and a method for fabricating the same.
Hetero-junction bipolar transistors have been used as communication devices such as mobile communications requiring high-speed operation characteristic and high integration because hetero-junction bipolar transistors have excellent high-speed operation characteristic and high current driving ability, compared to Si homo-junction bipolar transistors. Specifically, in recent years, a hetero-junction bipolar transistor (which will be herein referred to as an “HBT”) of which cutoff frequency is over 100 GHz has been achieved by making a bipolar transistor include a hetero-junction structure such as Si/SiGe and Si/SiGeC.
As a known example of methods for fabricating such a hetero-junction bipolar transistor, a method disclosed in Reference 1 (Japanese Laid-Open Patent Publication No. 9-186172) has been known.
Features of the known method for fabricating an HBT are that ion implantation is performed to an external base layer (a polycrystalline SiGe film) and that influence of lateral diffusion of an impurity which has been ion-implanted into a polysilicon emitter electrode (an emitter contact layer) is reduced by providing a spacer. In this case, the thickness of a polysilicon film of the polysilicon emitter electrode is about 140 nm. As for conditions for additional ion implantation into the external base layer, the acceleration energy is 60 keV and the dose is 2×1015 cm−2 when boron (B) ions are implanted and the acceleration energy is 30 keV and the dose is 1×1015 cm−2 when boron fluoride (BF2) ions are implanted.